This invention relates in general to a motion analysis system which records images of an event at a fast frame rate and plays back the images of the event at a slower frame rate so that the event may be analyzed. More particularly, this invention relates to a solid state motion analysis system having a video trigger circuit for changing the mode of operation of the motion analysis system in response to a change in an image characteristic of selected images of the event.
Motion analysis systems are useful for analyzing rapidly changing events. One type of motion analysis system records a great number of images during an event at a high or fast image frame rate and reproduces the image frames more slowly at a lower frame rate. Thus, any movement occurring during the event may be analyzed in a step by step progression. Applications for a motion analysis system include, malfunctions in high speed machinery, movements of an athlete, testing of safety equipment, shattering of an object, etc. One type of motion analysis system is disclosed in commonly assigned U.S. Pat. No. 4,496,995 issued Jan. 29, 1985. As disclosed in the latter patent, the motion analysis system/fast frame recorder includes a video camera, a variable speed processor and a video display monitor. The camera is read out in block format so that, a plurality of lines of video information that correspond to rows of photosites in the camera solid state imager, are simultaneously recorded on magnetic tape in parallel longitudinal tracks. During playback, the magnetic tape is played back at a reduced tape speed. A plurality of parallel video signals reproduced from parallel tracks on the tape are processed into a serial video signal which may be used with standard video monitors. A magnetic tape motion analysis system is advantageous, because of the ability to record a large number of image frames and because of the nonvolatility of the image storage. However, there are limitations to magnetic tape recording. Thus, magnetic tape motion analysis systems tend to be costly, since, in recording and reproducing a plurality of parallel video signals, separate record and reproduce signal processing circuitry must be provided for each video signal channel. Moreover, since the video signals are recorded directly on magnetic tape in an analog format, picture quality is degraded significantly due to induced flutter and other noise, due to reduced bandwidth and increased phase distortion and due to imprecisely recorded pixel signal values.
In many applications where the use of a motion analysis system is appropriate, the event to be analyzed may occur after a long period of static activity in the scene under analysis. Due to the inherent recording length constraints of a magnetic tape motion analysis system, such a system's ability to capture randomly occurring events may require the recording of a large number of image frames which are unnecessary for the analysis of the event. During playback, the unwanted images must be scanned before images relating to the event can be analyzed, resulting in a waste of time, money and recording tape. Moreover, certain events may be incapable of being recorded due to the length of elapsed time between recordable events.